Various exhaust gas mufflers have been known in the art. One of the issues when developing exhaust gas mufflers is to provide adequate catalytic treatment of the exhaust gas at a low gas counter pressure. A solution is disclosed in U.S. Pat. No. 6,393,835 that relates to an exhaust gas muffler on an internal combustion engine in motor chain saw. The exhaust gas muffler includes a housing that is assembled of two housing shells. The one housing shell has an exhaust gas inlet and the other housing shell has an exhaust gas outlet. An inner wall as well as a catalytic converting element is provided in the inner space of the muffler housing. The catalytic converting element is mounted between the exhaust gas inlet and the exhaust gas outlet. In order to ensure an adequate catalytic converting treatment of the exhaust gas at low gas counter pressure, it is provided to divide the entering exhaust gas flow and to conduct at least one of these component flows in contact with the catalytic converting element. The component flows are brought together and mixed with other before exiting from the muffler housing. However, not all exhaust gas is treated and the construction is relatively spacious.
In U.S. Pat. No. 5,732,555 a catalytic converter is disclosed for treating the exhaust gases of an internal combustion engine which is less expensive and easier to manufacture than other catalytic converters. This multi pass catalytic converter/muffler uses a single catalytic support bed without increasing the overall size of the catalytic converter/muffler. The outer surface area of the catalytic support bed is disposed adjacent to the outer wall of the catalytic converter housing, with only the mat in between. Secondary air may be provided upstream before the exhaust gases make their first pass through the catalytic support bed, or after the first pass but before the second pass or even after the second pass. Again, the construction is relatively large.
An invention to reduce high exhaust emission output levels is disclosed in U.S. Pat. No. 5,521,339, describing a muffler for coupling to an exhaust port of an internal combustion engine which includes a housing, a first hollow body within the housing, a catalyzer within the first hollow body, and a second hollow body within the housing. The first hollow body has an inner surface defining a first chamber and an inlet adjacent the exhaust port to admit the exhaust gas into the first chamber. The exhaust gas is exothermally treated as it flows through the catalyst in the first chamber in a direction away from the engine and passes through an outlet of the first hollow body to a second chamber. The second chamber is formed by an inner surface of the second hollow body and an outer surface of the first hollow body. The treated exhaust gas flows through the second chamber in a direction toward the engine over the outer surface of the first hollow body where a thermal reaction takes place and/or further emission reduction takes place by a catalytic coating on the outer surface of the first hollow body. The treated exhaust gas passes through an outlet of the second hollow body to a third chamber. The third chamber is formed by an outer surface of the second hollow body and an inner surface of the housing. After expanding and mixing in the third chamber, the exhaust gas is expelled from the third chamber through an outlet of the housing adjacent the engine. The volume downstream of the catalyst is however small resulting in high temperatures in the catalyst. The thermal endurance of catalysts is normally low.
EP 1 600 613 discloses a muffler for attachment to an engine that includes an inlet for receiving exhaust gases into the muffler, a catalyst assembly located within the muffler, and a fastener tube for fastening the muffler to the engine. A fastener tube cover covers the fastener tube and includes an outlet for exiting exhaust gases. The outlet includes a directional louver that directs the exiting exhaust gases. The fastener tube cover can retain a spark arrestor, which maintains maximum spark particle size in the exiting exhaust gases. One issue with this muffler is length of life for the catalyst resulting from high temperatures.